This randomized phase III trial studies doxorubicin hydrochloride, cyclophosphamide, paclitaxel, and trastuzumab to see how well they work compared to combination chemotherapy alone in treating women with breast cancer that is human epidermal growth factor receptor 2 (HER2)-positive and has spread to the lymph nodes or high-risk and has not spread to the lymph nodes. Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Monoclonal antibodies such as trastuzumab can locate tumor cells and either kill them or deliver tumor-killing substances to them without harming normal cells. It is not yet known whether combination chemotherapy is more effective with or without trastuzumab in treating breast cancer.

This randomized phase III trial studies the best individual therapy for women who have node-negative, estrogen-receptor positive breast cancer by using a special test (Oncotype DX), and whether hormone therapy alone or hormone therapy together with combination chemotherapy is better for women who have an Oncotype DX recurrence score of 11-25. Estrogen can cause the growth of breast cancer cells. Hormone therapy may fight breast cancer by blocking the use of estrogen by the tumor cells or by lowering the amount of estrogen the body makes. Drugs used in chemotherapy work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving hormone therapy together with more than one chemotherapy drug (combination chemotherapy) has been shown to reduce the chance of breast cancer recurrence, but the benefit of adding chemotherapy to hormone therapy for women with node-negative, estrogen-receptor positive breast cancer is small. New tests may provide information about which patients are more likely to benefit from chemotherapy.